The present invention relates generally to a multilayer film structure that is both sealable and peelable, and more specifically to a multilayer film having a heat-resistant layer located between the seal and core layers thereof.
Sealable film structures are known in the art. U.S. Pat. No. 5,500,265, for example, discloses a peelable film having a core layer comprising a olefin polymer, and a skin layer on at least one surface of the core layer. The skin layer comprises a blend of butylene polymer with another olefin polymer or a polymer of butylene and at least one other olefin. Also disclosed is a coating layer on the film.
U.S. Pat. No. 6,770,361 discloses a sealable and peelable film structure having a core layer, and a pair of outer layers, at least one of which is sealable. The core layer disclosed comprises a peelable blend comprising from 20%-80%, by weight, of a polyethylene and from 80%-20%, by weight, of a polyolefin incompatible with the polyethylene. The outer layers are comprised of thermoplastic polymers.
There remain, however, needs to be met in the field of sealable, peelable film structures. It occurs, on occasion, that the machinery used in the packaging and sealing of products commonly provided in sealed, peelable packaging will displace the seal layer of a multilayer film during the manufacturing process. In addition, even if the seal layer is not displaced, the machinery may otherwise disrupt the integrity of the seal layer. In either case, a layer separate from the seal layer is exposed when the package is sealed and the seal layer is sealed to that other layer. Alternatively, two non-seal layers may be inadvertently sealed to one another. In any event, the desired peel seal is not obtained and a consumer using the product will be unable to open the package as intended by the manufacturer. Instead, the separation or “tear” spreads to other layers of the multilayer film, resulting in what is known as a z-direction tear. Z-direction tears render a package more difficult to close properly, if the package is closeable at all, thereby limiting the freshness lifespan of the product contained therein. Eliminating z-direction tearing allows packages to be opened properly and, therefore, closed properly.
What is needed, therefore, is a film that reduces or eliminates inadvertent sealing of other than the seal layer(s).